Basic Units of Data Structure

A record (レコード) is one entry of data that groups the related data about a single subject, and it corresponds to a horizontal row in a table.

In a student roster, for example, one student's number, name, and grade taken together form one record. The highlighted row in the figure is one such record for a single student. The column (or set of columns) used to tell each record in a table apart is called the primary key (主キー), and it is chosen so that its value never repeats across records.

AnalogyIt is like a single card in an address file. One card holds one person's name, address, and phone number.

How to rememberThe English word record means a written account. Think of it as one note jotted down about a person or an event, and it ties naturally to the idea of a single entry.

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A field (フィールド) is each slot for data that makes up a record, and it corresponds to a vertical column in a table.

A single field lines up the same kind of data for every record, so a "Name" field holds only names. Each field is given a name and a data type set in advance, such as number, text, or date.

AnalogyThink of the vertical strip you trace down the "Phone" column of a roster for everyone. Whichever row you look at, that strip holds only phone numbers.

How to rememberField also means a plot of farmland. Just as a field grows only one crop, it is a place that holds only one kind of value.

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A data item (項目, also called データ項目) is each unit, such as "Name" or "Price," into which meaningful data is divided, and in a table it means almost the same thing as a field.

One record is expressed as a set of values for several data items. Deciding which data items to keep is the same as deciding how the table's columns are laid out.

AnalogyIt is like each heading in a household account book, such as "Date," "Item," and "Amount." Each heading decides what gets written down.

How to rememberBoth kanji in 項目 stand for the smaller divisions of a whole. Picture each line of a bulleted list.

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A table (テーブル) is a grid-shaped container that a relational database uses to hold data, with same-shaped records as rows and fields as columns.

Each table represents one kind of subject, such as students, books, or orders. A relational database consists of several tables, and each cell where a row and a column meet holds a single value.

AnalogyIt is like a class contact list. Each row is one person, the columns are name and phone number, and the whole sheet covers one class.

How to rememberBesides a dining table, the English word table also means a chart or list, the same table found in timetable.

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Hyō (表) is the native Japanese word for a table (テーブル), and it refers to the same container made of rows and columns.

When explaining relational databases, individual tables are often named by adding 表 to the subject, as in the "Students" table (“生徒”表). In the same way, row is used as another word for record, and column as another word for field.

AnalogyLike "restroom" and "bathroom," the names differ but they point to the same thing.

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A file (ファイル) is a body of data in which records of the same format are collected and saved as a single unit.

A file is saved under a name, and a program reads and writes the records inside by specifying that name. Before databases became common, each business program managed its data in its own dedicated files, so the same data easily ended up duplicated across several files.

AnalogyIt is like a binder of forms that all share the same layout. Each sheet inside is one record.

How to rememberAs an English verb, file means to put papers away in order, and as a noun it means the papers kept that way. Picture a bound stack of sheets.